dumpon man page on FreeBSD

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DUMPON(8)		  BSD System Manager's Manual		     DUMPON(8)

     dumpon — specify a device for crash dumps

     dumpon [-v] special_file
     dumpon [-v] off

     The dumpon utility is used to specify a device where the kernel can save
     a crash dump in the case of a panic.

     Calls to dumpon normally occur from the system multi-user initialization
     file /etc/rc, controlled by the “dumpdev” variable in the boot time con‐
     figuration file /etc/rc.conf.

     For most systems the size of the specified dump device must be at least
     the size of physical memory.  Even though an additional 64 kB header is
     added to the dump, the BIOS for a platform typically holds back some mem‐
     ory, so it is not usually necessary to size the dump device larger than
     the actual amount of RAM available in the machine.

     The dumpon utility will refuse to enable a dump device which is smaller
     than the total amount of physical memory as reported by the hw.physmem
     sysctl(8) variable.

     The -v flag causes dumpon to be verbose about its activity.

     Since a panic(9) condition may occur in a situation where the kernel can‐
     not trust its internal representation of the state of any given file sys‐
     tem, one of the system swap devices, and not a device containing a file
     system, should be used as the dump device.

     The dumpon utility operates by opening special_file and making a
     DIOCSKERNELDUMP ioctl(2) request on it to save kernel crash dumps.	 If
     special_file is the text string: “off”, dumpon performs a DIOCSKERNELDUMP
     ioctl(2) on /dev/null and thus instructs the kernel not to save crash

     /dev/{ad,da}?s?b  standard swap areas
     /etc/rc.conf      boot-time system configuration

     fstab(5), rc.conf(5), config(8), init(8), rc(8), savecore(8), swapon(8),

     The dumpon utility appeared in FreeBSD 2.1.

     Because the file system layer is already dead by the time a crash dump is
     taken, it is not possible to send crash dumps directly to a file.

BSD				 May 12, 1995				   BSD

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